As a vehicle such as an automobile, a vehicle that employs only an engine such as a gasoline engine and a diesel engine (an internal combustion engine) as a driving power source for running (a conventional vehicle) is generally known. Recently, a hybrid vehicle, an electric vehicle (EV), a fuel cell vehicle, or a similar vehicle has been developed and put to practical use as a vehicle that promotes environment protection.
Among these vehicles, the hybrid vehicle includes an engine and an electric motor (for example, a motor generator or a motor). The electric motor is driven by electric power generated by an output from the engine and electric power stored in a battery (an electric storage device). The use of one of or both of the engine and the electric motor as a source for driving power for running ensures running the hybrid vehicle.
The hybrid vehicle includes a power switch to change between start and stop of a hybrid system (a driving power source). When, for example, the power switch is operated with a brake pedal operated, the hybrid system starts. If the power switch is operated during running of the vehicle, the hybrid system stops.
Note that, in a hybrid vehicle, there is the following technique described in Patent Literature 1 as a technique for starting or stopping a hybrid system. In the technique described in Patent Literature 1, when a vehicle start/stop switch is operated to an engine stop position (Off position or Ready-Off) while the vehicle is running at a high speed, an engine stop is prohibited. By so doing, the amount of discharge of a battery does not exceed an upper limit discharge amount. Thus, the battery is protected.